As well known to motorists, a flooded engine at the very least creates an inconvenience, often incurs a cost of road aid, and sometimes exposes the car and its passengers to unnecessary safety risks. This is in addition to the unnecessary degredation to the life and operation of the engine in the form of fouled spark plugs, cylinder walls washed of their lubricants, and accelerated engine wear due to breakdown of the lubricants themselves. It is therefore highly desirable to enhance engine starting operation while at the same time decreasing the risk of engine flooding.
Conventional spark-ignited internal combustion engines are cranked at about 30 RPM during starting which is markedly lower than the 600 RPM idling speeds when started. Therefore, less air is inhaled during starting resulting in poor fuel atomization, increased wetting of the walls of the intake manifolding by the raw fuel, and generally more marginal ignition conditions. Moreover, such effects become more pronounced with decreasing starting temperatures.
Conventionally, to compensate for these conditions, the air fuel mixture is enriched during cranking as a function of decreasing temperature and battery supply voltages. In the case of one conventional fuel injected eight cylinder engine, it has been found that, in order to start the engine within two seconds of cranking, the widths of the injected fuel pulses have to be extended from normal operating values of about 10 milliseconds to starting values of about 35 milliseconds when starting at -20.degree. F.
As the widths of the start pulses increase so does the risk of flooding the engine. To minimize this risk, the starting pulses are calibrated to be leaner than optimum at each temperature, resulting in longer cranking times, greater expenditure of battery power, etc. To the extent that such longer cranking might consume all the effective cranking power, the engine might not start where it otherwise might have started. It is therefore desirable to start the engine using the richest mixture possible in the shortest cranking time.
The risk of flooding thus increases with decreasing temperature not only because of the required wide variation in the quantity of fuel required over the service range of temperatures but also because of the comparatively tight tolerance on the quantity of fuel required at each temperature. Moreover, since these quantities are based on assumed cranking speeds, the risk of flooding is further increased by factors affecting cranking speeds, such factors including variations in available battery voltages due to aging and temperature. It is therefore desirable to start an internal combustion engine using the richest fuel mixture possible without flooding the engine.
Compared to conventionally-carburetted internal combustion engines, those that are fuel injected experience an inherently lower risk of inadvertently flooding during starting. Such fuel injection systems include those disclosed in my commonly-assigned U.S. Pat. No. 3,734,068 and RE No. 29,060, the disclosures of which are hereby expressly incorporated herein by reference. As disclosed therein, the widths of the fuel pulses are closely tailored to general engine operating conditions, and, in particular, to cold start conditions. Moreover, even though very low battery voltages are still experienced when starting in cold weather, the effect of the resulting low supply voltages on the injector drive circuits may be reduced by using injector drive circuits of the type that use more of the available supply voltage to activate the injectors. Such injector drive circuits may be of the type that do not use the external resister conventionally connected series with each injector to protect it from an inadvertent short circuit. This type of circuit includes those disclosed in my commonly-assigned co-pending U.S. Pat. application No. 370,140 and U.S. Pat. No. 3,725,678 representing a continuation and division respectively of my now abandoned patent application No. 130,349 filed Apr. 1, 1971, the disclosures of each such case being hereby expressly incorporated herein by reference.
Finally, the risk of flooding may be further reduced by using fuel injectors effecting a finer and more uniform atomization. Such fuel injectors may be of the type disclosed in the commonly-assigned patent to Kiwior 4,030,668 and Kiwior et al 4,057,190, the disclosures of which are hereby expressly incorporated by reference.
However, even with such improved fuel injection systems, injector drive circuits, and fuel injectors, the electrical parameters of each system component may nevertheless shift with aging and temperature. Such shifts in electrical parameters could shift the widths of the computed start pulses outside their tolerances. As a result, injectors could stay open for the entire period available for fuel injection rather than just for the start pulse portion of such period that would have been computed if the parameters had not shifted and/or the battery supply dropped more than expected. To avoid the consequences of flooding, it is therefore desirable to detect an indication of incipient flooding in the form of the quantity of fuel injected during starting and then to use this information to either inhibit or otherwise attenuate further fuel injection.
As an example of one type of the latter circuit, the patents to Moulds et al No. 3,628,510 and Barr 3,616,784 both disclose a cranking enrichment circuit that adds constant-width enrichment pulses at a frequency varying inversely with engine temperature to conventionally computed variable width pulses generated in synchronization with engine rotation. Such variable-frequency constant-width enrichment pulses are added from the commencement of cranking when the charging of a capacitor is also commenced to when the capacitor voltage exceeds a predetermined reference. While the intervening time is an indication of the quantity fuel injected during each cranking interval, this time is at best only an approximation of the actual quantity of fuel injected. The approximation is based on the assumptions that there are no changes with temperature, age, etc. from the calibrated values of the frequency or widths of the basic fuel pulses to which the enrichment pulses are added, or even the basic cranking speeds. In other words, any unmatched shift in the values of these or other system parameters from their calibrated values increases the difference between the quantity of fuel actually injected during starting and the quantity that might be inferred from the time elapsed from beginning of cranking to when the capacitor voltage exceeds a reference threshold. Therefore, unless the Moulds/Barr reference threshold is set to include a sufficient margin of leanness from an incipient flood condition, the cranking enrichment circuits might not predict and prevent flooding in situations where flooding might otherwise occur. And even if the threshold were set with a sufficient margin of leanness, the resulting longer cranking times incurred might deplete the battery faster in the very cold start temperatures where flooding is most probable. In that case, the engine might not start, not because it has flooded, but because the remaining battery power is insufficient to adequately crank the engine.
It is therefore desirable to provide an anti-flood circuit utilizing a more direct indication of the quantity of fuel actually injected during cranking than the elapsed time from the beginning of cranking.